For production of an alpha-olefin polymer, especially an ethylene homopolymer or an ethylene/alpha-olefin copolymer, a method has heretofore been known to polymerize ethylene or copolymerizing ethylene with an alpha-olefin in the presence of a titanium-containing catalyst comprising a titanium compound and an organoaluminum compound or a vanadium-containing catalyst comprising a vanadium compound and an organoaluminum compound.
Catalysts comprising zirconium compounds and aluminoxanes have recently been proposed as a new Ziegler-type olefin polymerization catalyst.
Japanese Laid-Open Patent Publication No. 19309/1983 describes a process for polymerizing ethylene and at least one C.sub.3 -C.sub.12 alpha-olefin in the presence of a catalyst composed of a transition metal-containing compound represented by the following formula EQU (cyclopentadienyl).sub.2 MeRHal
in which R is cyclopentadienyl, C.sub.1 -C.sub.6 alkyl, or halogen, Me is a transition metal and Hal is halogen, and a linear aluminoxane represented by the following formula EQU Al.sub.2 OR.sub.4 (Al(R)--O).sub.n
in which R is methyl or ethyl, and n is a number of 4 to 20, or a cyclic aluminoxane represented by the following formula ##STR1## in which R and n are as defined above, at a temperature of -50.degree. C. to 200 .degree. C.
Japanese Laid-Open Patent Publication No. 95292/1984 describes an invention relating to a process for producing a linear aluminoxane represented by the following formula ##STR2## in which n is 2 to 40, and R is C.sub.1 -C.sub.6, and a cyclic aluminoxane represented by the following formula ##STR3## in which n and R are as defined. This patent publication discloses a specific example in which methylaluminoxane, for example, produced by the process of this patent publication is mixed with a bis(cyclopentadienyl) compound of titanium or zirconium, and an olefin is polymerized in the presence of the mixture.
Japanese Laid-Open Patent Publication No. 35005/1985 discloses a process for producing an olefin polymerization catalyst, which comprises reacting an aluminoxane represented by the following formula ##STR4## in which R is C.sub.1 -C.sub.10 alkyl, and R.sup.O is R.sup.1 or is bonded to represent --O--. with a magnesium compound, chlorinating the reaction product, and treating the chlorinated product with a compound of Ti, V, Zr or Cr. This patent publication describes that the above catalyst is especially suitable for the copolymerization of a mixture of ethylene and a C.sub.3 -C.sub.12 alpha-olefin.
Japanese Laid-Open Patent Publication No. 35006/1985 discloses a combination of (a) a mono-, di- or tri-cyclopentadienyl compound of two or more different transition metals or its derivative and (b) an alumoxane (aluminoxane) as a catalyst system for production of a reactor blended polymer.
Japanese Laid-Open Patent Publication No. 35007/1985 describes a process for polymerizing ethylene alone or together with an alpha-olefin having at least 3 carbon atoms is polymerized in the presence of a catalyst system comprising a metallocene and a cyclic aluminoxane represented by the following formula ##STR5## in which R is an alkyl group having 1 to 5 carbon atoms, and n is an integer of 1 to about 20, or a linear alumoxane represented by the following formula ##STR6## in which R and n are as defined above.
Japanese Laid-Open Patent Publication No. 35008/1985 discloses that by using a catalyst system containing at least two metallocenes and an alumoxane, polyethylene or an ethylene/C.sub.3 -C.sub.10 alpha-olefin copolymer having a broad molecular weight distribution is produced.
The catalysts formed from transition metal compounds and aluminoxanes as proposed in these prior art references have much higher polymerization activity than catalyst systems formed from transition metal compounds and organoaluminum compounds known heretofore. But most of the catalyst systems proposed in the prior art are soluble in the reaction systems, and are used in many cases in a solution polymerization system. As a result, the viscosity of the polymer solution becomes very high, the polymer obtained by after-treatment of the solution has a low bulk density, and it is difficult to obtain polymers having excellent powder characteristics.
On the other hand, attempts have also been made to polymerize olefins in a suspension polymerization system or a vapor-phase polymerization system by using catalysts comprising the above transition metal compound, or the aluminoxane or both supported on a porous inorganic oxide carrier such as silica, silica-alumina or alumina.
For example, the above cited Japanese Laid-Open Patent Publications Nos. 35006/1985, 35007/1985 and 35008/1985 describe that transition metal compounds and aluminoxanes can be used as catalysts supported on silica, silica-alumina, alumina, etc.
Japanese Laid-Open Patent Publications Nos. 106808/1985 and 106809/1985 propose a process for producing a composition comprising a polyethylene-type polymer and a filler which comprises polymerizing ethylene or copolymerizing ethylene and an alpha-olefin in the presence of a product obtained by contacting treatment of a highly active catalyst component containing titanium and/or zirconium soluble in a hydrocarbon solvent and a filler, an organoaluminum compound, and a filler having affinity for polyolefins.
Japanese Laid-Open Patent Publication No. 31404/1986 proposes a process in which ethylene is polymerized, or ethylene and an alpha-olefin are copolymerized, in the presence of a mixed catalyst composed of a transition metal compound and a product obtained by reacting a trialkyl aluminum with water in the presence of silicon dioxide or aluminum oxide.
Japanese Laid-Open Patent Publication No. 276805/1986 proposes a process in which an olefin is polymerized in the presence of a catalyst comprising a reaction mixture obtained by reacting a zirconium compound and an aluminoxane with a trialkyl aluminum, and reacting the reaction mixture further with an inorganic oxide having a surface hydroxyl group such as silica.
Japanese Laid-Open Patent Publications Nos. 108610/1986 and 296008/1986 propose a process in which an olefin is polymerized in the presence of a catalyst obtained by supporting a transition metal compound such as a metallocene and an aluminoxane on a support such as an inorganic oxide. Japanese Laid-Open Patent Publication No. 296008/1986 discloses a method in which the above catalyst is prepared by recovering the reaction mixture from the liquid by vacuum evaporation or decantation.